The present invention relates to a process for improving the coefficient of traction and a traction drive fluid composition for use therein More particularly, it is concerned with a process for improving the coefficient of traction between at least two relatively rotatable elements in a torque transmitting relationship and a traction drive fluid composition for use therein
A traction drive fluid is a fluid to be used in traction drives (friction driving equipment utilizing rolling contact), such as continuously variable transmissions for cars or industrial machines and hydraulic machines. In general, such traction drive fluids are required to have a high traction coefficient, high stability against heat and oxidation and furthermore to be inexpensive.
In recent years, investigations have been made to reduce the size and weight of the traction drive unit, particularly for use in cars. With this miniaturization and reduction in weight of the traction drive unit, the traction drive fluid to be used in such traction drive units is now required to have such high performance that it be used under severe conditions, particularly to have a high traction coefficient, a suitable viscosity, and high stability against heat and oxidation in a stabilized manner over a wide temperature range of from low temperature to high temperature (specifically from about -30.degree. C. to 140.degree. C).
Various traction drive fluids have been proposed as described in, for example, Japanese Patent Publication Nos. 338/1971, 339/1971, 35763/1972, 42067/1973, 42068/1973, 36105/1978, 42956/1987, 15918/1986, 44918/1986, 27838/1983, and 44391/1985. These traction drive fluids, however, fail to satisfy the requirements as described above. For example, compounds having a high traction coefficient at high temperatures produce a large agitation loss because of high viscosity thereof and, therefore, have disadvantages in that the transmission efficiency is low and start-up property at low temperatures is poor. On the other hand, compounds which are of low viscosity and are excellent in transmission efficiency have a low traction coefficient at high temperatures, and as the temperature rises, their viscosities drop excessively, causing troubles in lubricity of the traction transmission unit.